This invention relates generally to fluid atomizers and is particularly directed to a rotary atomizer which provides a high degree of control over droplet size and spray pattern.
Crop spraying is a widespread method for protecting crops from pests as well as for restricting the growth of other, competing forms of plants. Early approaches to crop spraying involved the mixing of a pesticide with water and discharging the mixture under pressure through a hydraulic nozzle. Upon discharge, the motion of the mixture droplets is affected by wind velocity prior to deposit upon the soil and/or crops. So long as the drift is uniform, i.e., the same for all droplets, the location of incidence of the mixture droplets can be fairly accurately controlled. However, where the droplets differ substantially in size, the smaller droplets will be influenced by the surrounding air currents in a manner different from that of the larger droplets and will thus be deposited in locations different from those upon which the larger drops are incident. Irregularities in the spraying pattern will cause overspraying in some areas and inadequate spraying as well as failure to deposit the fluid mixture on other areas. The early use of water as a medium for transport of the pesticide gave way to the use of various oils such as vegetable oils which tend to provide more uniform droplet size. However, hydraulic nozzles still suffer from the inability to control droplet size and to accurately spray the pesticide mixture over the intended area.
The hydraulic nozzle approach is increasingly being replaced by Controlled Droplet Applicators (CDA) which offer the advantage of droplet size control and thus increase the effectiveness of pesticide application. CDA's generally include an electrically or hydraulically actuated motor for rotating a generally circular element upon and over which the mixture to be sprayed is caused to flow. The rotating element, which is frequently in the form of a cup, discharges the mixture in a radial direction at high speed after breaking it up into small droplets. Generally, a high speed air flow is directed across the edge of the rotating discharge device to facilitate removal of the mixture from the rotating atomizer and to displace it radially with respect thereto. A generally circular spray pattern is thus produced, with a plurality of such CDA's providing continuous coverage over the length of a spray boom to which the CDA's are mounted by positioning the various spray patterns in an overlapping manner.
While CDA's have generally improved the atomization of the sprayed chemical, increasing its deposit on larger intended areas and thus reducing the amount of chemical required, even this approach suffers from performance limitations. For example, prior art CDA's do not provide uniform spray distribution because of fluid flow characteristics on and about its rotary atomizer. This undesirable nonuniform spray distribution, or streaking, may be caused by the interaction of the air flow with the formed droplets, the manner in which the droplets separate from the rotary atomizer, an irregular and nonuniform fluid flow within the rotating atomizer, or any number of other fluid flow factors or air flow characteristics of the CDA. For example, it is not enough to break the spray chemical into the smallest possible droplets in order to maximize the area of coverage. If all of the minute droplets are not of the same general size, their distribution within the spray will also be nonuniform and the sprayed area will be covered in an irregular manner by the deposited mixture.
The present invention is intended to overcome the aforementioned limitations of the prior art by providing a rotary atomizer for forming droplets of uniform size which, in turn, are distributed uniformly throughout the entire spray pattern for more even distribution of the sprayed mixture. The rotary atomizer of the present invention uses a single rotating element to form droplets of essentially the same size in a circular pattern and then directs a high velocity air flow over the thus formed droplets which are then widely dispersed in a uniform manner.